From: Ian Jackson <iwj@xenproject.org>
To: Jan Beulich <jbeulich@suse.com>
Cc: "Tim Deegan" <tim@xen.org>,
"George Dunlap" <george.dunlap@citrix.com>,
"Andrew Cooper" <andrew.cooper3@citrix.com>,
"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH][4.15] x86/shadow: suppress "fast fault path" optimization without reserved bits
Date: Thu, 25 Feb 2021 13:20:13 +0000 [thread overview]
Message-ID: <24631.41997.596809.646522@mariner.uk.xensource.com> (raw)
In-Reply-To: <dae5479e-9974-334b-7f4f-e4194e435aaa@suse.com>
Jan Beulich writes ("Re: [PATCH][4.15] x86/shadow: suppress "fast fault path" optimization without reserved bits"):
> As to 4.15: Without this shadow mode simply won't work on such (new)
> hardware. Hence something needs to be done anyway. An alternative
> would be to limit the change to just the guest-no-present entries (to
> at least allow PV guests to be migrated), and refuse to enable shadow
> mode for HVM guests on such hardware. (In this case we'd probably
> better take care of ...
Thanks for this explanation.
It sounds like the way you have it in this proposed patch is simpler
than the alternative. And that right now it's not a regression, but
it is needed for running Xen on such newer hardware.
> The main risk here is (in particular for the MMIO part of the change
> I suppose) execution suddenly going a different path, which has been
> unused / untested (for this specific case) for years.
That's somewhat concerning. But I think this only applies to the new
hardware ? So it would be risking an XSA but not really risking the
release very much.
I think therefore:
Release-Acked-by: Ian Jackson <iwj@xenproject.org>
Ian.
next prev parent reply other threads:[~2021-02-25 13:20 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-25 13:03 [PATCH][4.15] x86/shadow: suppress "fast fault path" optimization without reserved bits Jan Beulich
2021-02-25 13:11 ` Jan Beulich
2021-02-25 13:20 ` Ian Jackson [this message]
2021-02-25 13:25 ` Jan Beulich
2021-02-25 13:17 ` Ian Jackson
2021-02-25 13:30 ` Jan Beulich
2021-02-26 17:07 ` Tim Deegan
2021-03-01 8:10 ` Jan Beulich
2021-03-01 17:30 ` Ian Jackson
2021-03-01 17:34 ` Andrew Cooper
2021-03-01 17:43 ` Ian Jackson
2021-03-02 10:22 ` Jan Beulich
2021-03-02 12:32 ` Ian Jackson
2021-03-02 13:17 ` Jan Beulich
2021-03-02 10:12 ` Jan Beulich
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